In the printing and paper making industries, heated rollers are commonly used to feed paper sheets and simultaneously perform some processing step on the paper. For example, an heated roller may serve as a pressure roll fuser for electrographic copiers, or as a calendar in making paper. In such applications, the roller is supported by gudgeons, also referred to as endcaps or journals, and is rotated by a drive mechanism connected to the roller through the gudgeons.
Gudgeons attached to fuser rollers perform many functions and so must be constructed to perform them with minimum failure. For example, gudgeons transmit rotational motion from the copier drive mechanism to the roller; they allow the bearing to fit over the gudgeon so that smooth rotational motion is obtained; they must be able to withstand fusing temperatures up to 450.degree. F. without degrading or affecting performance, and; they must be good thermal insulators so that heat transmitted to the bearings and to the frame is minimized. Exposure to high temperatures reduces bearing life.
Heat through the surface of the roller accomplishes the desired fixing of toned images to the sheets or calendering of the paper. In order to decrease heat losses through the ends of the heated roller and to the surrounding environment, it is desirable to construct the roller surface of one material having a high thermal conductivity (such as metal) and the gudgeons forming the ends of the roller of another material having a low thermal conductivity (such as an organic material). Materials of low thermal conductivity, however, generally do not match the metal roller in its physical characteristics of strength, stiffness or thermal expansion. Suitable measures must be taken to minimize the effect of these differences and provide gudgeons that will operate over extended temperature ranges without loosening or becoming eccentric and without inducing excessive stresses in the roller.
Historically, gudgeons have been manufactured with all plastics, such as thermoset epoxy, and thermoset polyimides such as Kinel.TM. 4504, Fibrite PI-740 & PI-755. The major problem with these materials is that the resin degrades, especially when in contact with the metal core. Degradation is generally characterized by shrinkage which leads to motion of the gudgeon in relation to the core which in turn leads to transmission of torque and rotational motion through the gudgeon. This affects fusing performance to the extent that improper fusing occurs and the fuser roller must be replaced. Gudgeons may also be made of metal such as aluminum and steel, including stainless steel, but with the design of the present invention, the roller or ball bearings would require special lubricant and this would significantly increase the cost of the bearings.
Further problems arise because repetitive heating and cooling of the roller frequently cause the bolts to relax the coupling between the gudgeon and roller or ultimately to fracture.
Several configurations of heated rollers and their end gudgeons are disclosed in Research Disclosure Bulletin, Item 13027, Vol. 130, page 23-24, "Internally heated roller construction" published Feb. 10, 1975 in Hampshire, United Kingdom. These configurations are designed to help minimize the problems outlined above, but the durability of gudgeons continues to be a problem. What is needed, then, is an improved gudgeon which prevents substantial heat loss from the ends of a heated roller and which will not degrade or shrink or lose its close fit to the roller core upon repetitive heating and cooling.